Hybrid junctions, which have been widely discussed in the applicable literature, are extensively used in various radar balanced-circuit configurations, including balanced mixers, single-sideband modulators, phase and amplitude monopulse comparators, frequency multiplexers and constant impedance filters, (see e.g. Radar Handbook, Skolnik, Chapter 8).
Several useful forms of hybrid junctions are well known including the hybrid ring or "rat-race". Each form can generally be implemented in waveguide, coaxial line or stripline media.
The basic hybrid ring comprises a closed loop transmission line essentially six quarter wavelengths in length. Four ports on the ring are spaced 60 degrees apart geometrically and one quarter wavelength apart operationally. For an ideal hybrid ring, a signal input to port 1 divides equally between ports 2 and 4 with a 180 degree phase difference, whereas a signal input to port 3 divides equally between the same ports 2 and 4 with a zero phase difference.
The prior art is replete with variations of the basic hybrid ring. One such prior art disclosure describing a hybrid ring used as a mixer, is contained in U.S. Pat. No. 4,031,472. That patent reviews earlier devices and discloses an improved hybrid ring structure which allegedly avoids certain defects of the earlier devices; i.e. (1) the inability to derive an intermediate frequency (IF) signal in the physical plane of the hybrid and (2) the loss of output power as the IF frequency increases.